1. Field of the Invention
The present invention relates to a key top used as a pushbutton switch for various mobile communication devices such as a mobile phone and an automobile telephone, a remote control, or car-mounted electronic equipment.
2. Description of the Related Art
As a material for a key top for a pushbutton switch of various mobile communication devices and electronic equipment, such as a mobile phone and a remote control, resins are mainly used for reasons such as a satisfactory sensation of an operation and rich design variations. In terms of enhancement of design, there is a demand for a sensation of a metal-type material with lustrousness of metal (in the present specification, referred to as a “sensation of metal”) and illumination of a display portion displaying a letter, a symbol, or the like.
In order to satisfy the above-mentioned demand, in the case of providing a sensation of metal to a key top by utilizing a resin material, a key top made of a resin is produced by a following method in which a metal layer is formed in a desired position of the surface of a key top made of a resin by vapor deposition or sputtering (first prior art) or a method in which a resin to be plated with metal and a resin that is not to be plated with metal are subjected to coinjection molding, whereby a plating layer is provided on the resin to be plated with metal (second prior art).
Alternatively, a key top made of a resin has also been produced by a method in which a coating with a sensation of metal is applied (third prior art) or a method in which an electroplating layer formed on the surface of a resin to be plated with metal is etched with a laser to form a letter, a symbol, or the like (fourth prior art).
However, according to the method of the first prior art, the metal layer formed by vapor deposition or sputtering is thin. Therefore, when a key top made of a resin is repeatedly pressed down, the metal layer wears away and may eventually disappear. In order to solve this problem, the surface of the metal layer is coated with a protective layer, the metal layer is formed on the reverse surface of a flat resin film, and the resultant film is curved along the surface of a key top made of a resin to be integrated with a key top body, and the like. According to the former method, dust is likely to adhere during coating. According to the latter method, the metal layer is likely to be cracked when the resin film is curved. In both methods, the yield is poor and the cost is high.
According to the method of the second prior art, the display portion is designed by coinjection molding. Therefore, a display portion with minute and complicated designs cannot be realized and the cost is high.
According to the method of the third prior art, compared with the case where the metal layer is formed by plating, it is difficult to provide a smooth mirror surface, and wear resistance is not satisfactory. According to the method of the fourth prior art, unless a laser treatment is conducted after plating, it is difficult to form, in particular, letters containing an island portion isolated from the periphery, such as digits “9” and “0”, and it is difficult to adjust a laser output for forming a display portion without influencing regions on the periphery of a letter, a symbol, or the like.
JP 2000-207985 A describes a method of producing a key top by coating a desired site with a conductive ink, and plating the site coated with the conductive ink. However, according to this method, in order to decrease a resistance of the conductive ink, it is required to use silver powder or copper powder, which makes the conductive ink expensive, resulting in a high cost.